Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1991-05-28
1993-02-02
Langel, Wayne
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423235, C01B 908
Patent
active
051836475
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for purifying nitrogen trifluoride gas, and more particularly, to a method for removing, in particular dinitrogen difluoride from nitrogen trifluoride gas.
BACKGROUND ART
Nitrogen trifluoride (NF.sub.3) gas has recently drawn attention as a dry etching agent for semiconductors and a cleaning gas for CVD apparatuses, and nitrogen trifluoride gas used for these purposes is required to be as highly pure as possible.
Nitrogen fluoride (NF.sub.3) gas may be produced by various methods, but nitrogen fluoride gas produced by any method mostly contains impurities such as nitrous oxide (N.sub.2 O), carbon dioxide (CO.sub.2), dinitrogen difluoride (N.sub.2 F.sub.2) and the like in a relatively large amount. Therefore, it is required to purify the NF.sub.3 gas so as to obtain a highly pure NF.sub.3 gas usable for the above-mentioned purposes.
As a method for purifying NF.sub.3 gas by removing these impurities, a method which comprises adsorbing and removing the impurities by means of an adsorbent such as zeolite and the like is known as one of the most efficient and simplest methods [Chem. Eng., 84,116 (1977), etc] However, when N.sub.2 F.sub.2 is present in the NF.sub.3 gas, the purification method by adsorption suffers the following drawbacks.
That is,
1) When N.sub.2 F.sub.2 is present, the adsorption ability of the other impurities such as CO.sub.2, N.sub.2 O and the like is extremely lowered.
2) When N.sub.2 F.sub.2 is present, NF.sub.3 is liable to be adsorbed to the adsorbent resulting in a loss of NF.sub.3 gas.
3) N.sub.2 F.sub.2 adsorbed to the adsorbent and thereby concentrated is liable to decompose and generate heat, and in an extreme case, an explosion is caused.
Therefore, when impurities in NF.sub.3 gas are to be removed by using an adsorbent such as zeolite and the like, it is necessary to remove N.sub.2 F.sub.2 in advance.
As a method for removing N.sub.2 F.sub.2 contained in NF.sub.3 gas, a method is known which comprises reacting N.sub.2 F.sub.2 with an aqueous solution of KI, HI, Na.sub.2 S, Na.sub.2 S.sub.2 O.sub.4, Na.sub.2 SO.sub.3 or the like in a reaction vessel [J. Massonne, Chem. Ing. Techn., 41, (12), 695 (1969)]. However, according to this method, it takes a relatively long time to remove N.sub.2 F.sub.2 completely and therefore the reaction vessel must be considerably large and a large amount of chemicals is also necessary.
As another known method for removing N.sub.2 F.sub.2, NF.sub.3 gas containing N.sub.2 F.sub.2 is passed through a catalyst packed bed formed by packing a reaction vessel with metal pieces or nets which has a sufficient reactivity capable of defluorinating N.sub.2 F.sub.2 such as heated stainless steel, carbon steel, copper, aluminum, zinc, lead, nickel, iron and the like, and thereby, when the NF.sub.3 gas is brought into contact with the metal pieces or net as a catalyst, the N.sub.2 F.sub.2 is decomposed on the surface of the metal pieces or net (U.S. Pat. No. 4,193,976). However, according to the present inventors' investigation, this method is liable to form metal fluorides on the surface of the metal pieces or net due to the reaction of the metal pieces with N.sub.2 F.sub.2. And the resulting metal fluorides are very fragile, are easily peeled off from the surface of the metal pieces and powdered. As a result, there is a drawback their that the powder clogs the packed bed and pipes and the like of the purification apparatus.
According to our investigation, when nickel is used as the metal pieces, the fluoride film is formed on the surface of the nickel pieces, but after the surfaces of the nickel pieces have become covered with the fluoride film, there is no exposed nickel metal surface remaining for the reaction with N.sub.2 F.sub.2 so that the nickel pieces naturally have lost the catalytic activity. Therefore, it is necessary to stop the operation periodically and substitute new nickel pieces for the old ones so as to newly pack the catalyst bed. Therefore, the operation is very complicated and more
REFERENCES:
patent: 4193976 (1980-03-01), Lileck et al.
patent: 4543242 (1985-09-01), Aramaki et al.
patent: 4804447 (1989-02-01), Sartori
patent: 4933158 (1990-06-01), Aritsuka et al.
patent: 4948571 (1990-08-01), Harada et al.
patent: 4960581 (1990-10-01), Harada et al.
patent: 4975259 (1990-12-01), Hyakutake et al.
patent: 4980144 (1990-12-01), Koto et al.
patent: 5084156 (1992-01-01), Iwanaga et al.
Harada Isao
Hokonohara Hisashi
Yamaguchi Toshiaki
Hendrickson Stuart L.
Langel Wayne
Mitsui Toatsu Chemicals Inc.
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